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§ 3.7 - DC-coupled 8 Channel Stereo Mixer

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Before you attempt this build, please:

This will help ensure that you will have the best possible experience, resulting in a build that works the way you expect it to.

This Mixer Block build is a DC-coupled, unity-gain, line-level, eight-channel, stereo mixer.

To power this with the Power Block, use the +/- 12 regulated Power Block build.

Tip: Unity gain (zero gain) is important here. This is because if all eight inputs to one of the op-amp channels reach 1.23 volts, in phase, all at once, then at unity gain the mixer will produce a 9.84 volt output level. This would be highly unlikely, but it is always at least possible.
If the mixer were to be built with more gain, then the output voltage would get too close to the op-amp's power supply rails (typically +/- 12 VDC), and distortion would result.
  1. C1—C2: .1 uF ceramic capacitor
  2. C3—C4 optional: ceramic capacitors, only needed for op-amps that require compensation
    TLO-72 and TLO-82 op-amps do not require compensation.
  3. C21—C22: 10 uF ceramic or other non-polarized capacitor
  4. R1—R18: 10 k-ohms 1/8th watt resistors
  5. Install 3-pin jumper J1 — use .100 inch (2.54 mm) header pins; do not close
  6. Install 2-pin jumper J2 — use .100 inch (2.54 mm) header pins; do not close
  7. Install 2-pin jumper J3 — use .100 inch (2.54 mm) header pins; close with a header jumper cap
  8. Install 2-pin jumper J4 — use .100 inch (2.54 mm) header pins; close with a header jumper cap
  9. U1: TLO-72 low-noise op-amp, can substitute TLO-82, or similar. Observe polarity. An IC socket is strongly recommended.
  10. Connectors, quantity 4, optional: 5.08mm (.200 in) Spacing, 2-pin PCB Mount Screw Terminal Blocks
  11. M3 mounting hardware, 4 mount points
Tip: If you would like to AC-couple the outputs while retaining the DC input coupling, remove the jumper caps from J3 and J4.
See also:Recommended Tools
Mounting to Wood Surfaces
Mixer Block Parts Sources
Wiring to Terminal Blocks


DC-coupled 8-channel Stereo Mixer, Build Guide


Mixer Block Schematic

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